288 reputation
9
bio website es.linkedin.com/in/izaera
location Madrid, Spain
age 39
visits member for 7 months
seen Jun 24 at 6:49

Apr
9
answered Will repeated rounds of SHA-512 provide random numbers?
Apr
7
comment Why are Fortuna entropy pools reset after a reseed?
You can download the paper from schneier.com/fortuna.pdf . Regarding the reset you are talking about: it does appear in the paper. I don't know the rationale behind it, but I suppose it has to do with avoiding poisoning of the pools. But the paper is very terse and does not give much reasons about the decisions made :-(.
Mar
31
comment Should an AES byte key generated with OpenSSL be converted to hex?
Makes more sense now. At least for me. I can't talk for the OP :-). Nevertheless, there's no need to worry: if he generates keys and converts them to ASCII hex and then uses them again directly without decoding it won't work. Mmm, I wonder if this development is being done for any commercial product....
Mar
28
accepted Why does Fortuna RNG use double SHA-256?
Mar
28
comment Why does Fortuna RNG use double SHA-256?
I still don't see how an extension attack could be used there but I guess it may help in getting some knowledge of the internal state of the RNG because what you are doing with the double hash is somewhat to avoid leaking the internal state of the digest.
Mar
28
comment Why does Fortuna RNG use double SHA-256?
Well, in fact that's the explanation. In Fortuna they calculate the new key for reseeds by doing SHA-256(oldKey || entropy) which is a construction vulnerable to length extension attacks. To avoid that HMAC (for example) does: hash(key || hash(key || message)). And another way to fix it is to do the double hashing. So I guess that's the reason.
Mar
27
comment Why does Fortuna RNG use double SHA-256?
BTW: the paper says nothing about why it chooses double SHA. The only reference to both SHA-256 and double SHA is in this sentence: "A typical hash function, like SHA-256, and hence SHAd-256, processes message inputs in fixed-size blocks". The rest of the paper it uses double SHA-256 for everything.
Mar
27
comment Why does Fortuna RNG use double SHA-256?
Thanks for the reply. I guess that affects RIPEMD-256 also. Am I wrong?
Mar
27
asked Why does Fortuna RNG use double SHA-256?
Mar
21
comment Should an AES byte key generated with OpenSSL be converted to hex?
@e-shusi: Can you elaborate (2) a little more? I can't see why storing something as hex may be different than storing it as binary. Sounds to me like saying that "Spanish is less secure than English" ;-).
Mar
20
comment CryptoJS.AES result always has same first few bytes?
Yes it would be. So what? It shouldn't matter. The algorithms and libraries used are always supposed to be known. Under the standard security models everything but the key is supposed to be public. Otherwise you are using security through obscurity.
Mar
20
answered CryptoJS.AES result always has same first few bytes?
Mar
20
comment Should an AES byte key generated with OpenSSL be converted to hex?
The key is nothing magic: it's just an array of bytes. You can represent an array of bytes as hexadecimal numbers, as characters, as a list of decimal numbers, encode them in base64, ... If you write it as hex numbers somewhere, then you should read them as hex and convert them to bytes again. This link may help stackoverflow.com/questions/1393238/…
Mar
19
comment Should an AES byte key generated with OpenSSL be converted to hex?
:-o SHA does not convert to hex. I think you should revisit your sources. You can convert to hex with any of the utilities Ruby gives you for that. Apart from that storing secret keys in the DB, doesn't seem a good idea.
Mar
13
comment distribution for a subset of md5
Disclaimer: I have never used it, just saw it some weeks ago by coincidence in the MacPorts repository.
Mar
13
comment distribution for a subset of md5
I'll go a little off-topic, but... How about using this? gnu.org/software/gperf
Mar
7
comment Does “use of SHA-256 in cryptography” imply use of SHA-256 both in HMAC and DH key exchange, assuming these are the only uses of hash in system?
SHA-256 is just a digest algorithm. It can be used wherever a digest can be used. There's no such term as "use of SHA-256 in cryptography", it's just a sentence.
Mar
7
comment Unpredictability vs randomness
I'll try something along the lines of github.com/bitwiseshiftleft/sjcl/blob/master/core/random.js (still have to look at it in detail) for getting entropy.
Mar
7
comment Unpredictability vs randomness
Got it :-). Thanks for the answers. There we some concepts I had not clear but now I think I have the whole image in mind. Now I have to decide what to implement. I'll probably use one standard approach like Yarrow or Fortuna to be safe and will try to get as much entropy as I can. The language I'm using is Google Dart and it has to work in server and client (in a browser). The server is not a problem, but getting entropy from a browser is a nearly impossible task (specially if you are offline and have no server).
Mar
7
accepted Unpredictability vs randomness